FI86054B - OVER ANCHORING FOR BOILING AV GLASSKIVA. - Google Patents

Description

1 86054

Method and apparatus for bending a glass sheet. - Förfarande och anordning för böjning av glasskiva.

The invention relates to a method for bending a glass sheet, the method comprising the following steps: - the glass sheet is heated in a bending furnace close to the softening temperature, to opposite sides.

The invention also relates to an apparatus for bending a glass sheet, the apparatus comprising: - a bending furnace with heating means for keeping the oven temperature high enough for bending the glass sheet, and - an annular mold with which the glass sheet to be bent is supported in the bending furnace.

The invention can be applied in connection with different types of furnace plants. One main type is one in which a glass sheet supported by an annular mold is transferred from one furnace compartment to another by increasing the temperature in successive furnace compartments. In the last compartment, the temperature becomes high enough for bending. The second • · .. main type is one in which the glass sheet is heated in a furnace with rollers and then moved e.g. from the rollers by an overhead vacuum lifter and lowered onto the imported ring mold, after which the bending can be performed with a ring --- · mold in the furnace or in a separate bending part. -tossa.

Regardless of the type of furnace used, the problem with bending with annular molds has been to control the temperature and bending of different areas of the glass sheet. If the temperature of the glass sheet is raised high enough to cause the difficult-to-bend edge areas 2,86054 to bend, the central area of the glass sheet will also soften so that it bends and hangs too downwards.

It is known to avoid this problem by applying a stronger heating effect to the edge areas of the glass sheet to allow them to bend sufficiently, but leaving the central area of the glass sheet much colder (e.g. 580 ° C) to avoid excessive bending and hanging down. However, this has the disadvantage that it is not possible to produce a properly tempered bent glass, because for tempering the entire area of the glass sheet would have to be heated above 600 ° C, preferably to a temperature of about 610 to 620 ° C.

The object of the invention is to provide a method and a device by means of which a glass sheet can be bent by an annular mold mainly by gravity, while the entire area of the glass sheet can be heated to a sufficient temperature for bending and also for tempering.

In particular, it is an object of the invention to provide a method and apparatus by which the gravitational bending of the entire area of a glass sheet can be controlled and controlled in a manner different from the conventional dependence of gravity and temperature. A further feature of the invention is the possibility to target the heating effect to critical areas of bending.

These and other objects of the invention, which appear in more detail below, can be achieved on the basis of the features set out in the appended claims.

In the following, some embodiments of the invention will be illustrated with reference to the accompanying drawings, in which Figure 1 shows a schematic axonometric view and a partially open section of an apparatus implementing the method according to the invention.

Figure 2 shows a bent glass sheet.

3,86054

Figures 3A to C show diagrammatically a side view of the bending of a glass sheet by the method and apparatus according to the invention at different stages of bending.

Figure 4 is a schematic side view of a mold structure with means for mechanically assisting the bending of a glass sheet.

Figure 5 is a schematic vertical section of an apparatus with which a bent and heated glass plate heated to the tempering temperature can be transferred to the tempering compartment.

Fig. 6 shows a schematic vertical section of a bending furnace in which the enhanced heating effect is applied to the edge areas of the glass sheet with the same blowing air, which generates a pressure difference supporting the glass sheet.

Fig. 7 is a schematic sectional view of another mold structure in which the air flow caused by the pressure difference acting on opposite sides of the mold is controlled by utilizing the holes or grooves 11 of the mold.

Fig. 8 shows a further schematic cross-section of a mold structure in which the pressure difference acting on opposite sides of the glass sheet is limited to the central area of the surface area of the glass sheet.

As can be seen in particular from Figures 1, 5 and 6, the furnace 1 is divided by a partition roof 3 into an upper furnace part 1.1 and a lower furnace part 1.2. Between the furnace parts or spaces 1.1 and 1.2 there is a pipe or duct system 4 with a fan 5 which transfers air from the upper furnace part 1.1 to the lower part 1.2. The suspended ceiling 3 has an opening 3.1 (see also Figures 3A, 7 and 8), above and at which point the annular mold 6 and the glass plate 7 supported by it are placed. The edges of the opening 3.1 may be more or less sealed against the annular mold 4 86054 tia 6 with the collar seal 3.2, the partition 3 and the collar 3.2 may be a metal plate. When the annular mold 6 with its glass plate 7 is placed on the opening 3.1 and the fan 5 transfers air from above the ceiling 3 to below, a pressure difference is created on opposite sides of the glass plate 7, which tends to support the glass plate 7. The differential pressure measurement 1a controls the desired fan power. difference and support effect on the glass sheet 7 is obtained. Thanks to this pressure difference, the entire glass sheet 7 can be heated to a temperature 610 to 620 ° C sufficient for tempering, without the central region C of the glass sheet, which is not supported by the ring mold, hanging downwards too much.

Critical bending areas B are formed in the end areas of the glass sheet and in the vicinity of the corners, where the deformation of the glass sheet and the required elongation are greatest. As shown in Figure 6, the air used to generate the pressure difference can be directed through the tubes 4.3 to these critical bending areas, whereby increased convection enhances the heating of these areas. Of course, the pressure caused by the blowing flow can also contribute to the fact that the pressure difference on opposite sides of the glass sheet varies in different areas of the surface. However, in the entire surface area of the glass sheet 7, the pressure P2 below is substantially higher than the pressure effect P1 above. In this case, the term "pressure effect" is to be understood broadly to include the reaction force of the flow impinging on the surface of the glass.

In the case of Fig. 3, in contrast to the conventional edge mold bending, a mold structure is shown, which provides a downward bending of the edge and corner areas of the glass sheet while raising the central area. The raising of the central area thus takes place by means of both the mold structure and the said pressure difference. Figure 3A shows a glass plate 7 in the initial stage of heating. In Figure 3B, the glass sheet has already bent almost into the shape of a mold. In this case, the air flow in the area of the edges of the glass plate from pressure P2 to pressure 5 86054

Pi has accelerated. This flow heats the edge areas of the glass sheet and helps them to bend downwards. However, the flow itself does not create a greater pressure difference in the edge regions than the pressure difference acting in the central region. In Fig. 3C, the bending is completed and the glass sheet can be subjected to tempering. The glass sheet can be transferred to the tempering compartment 2, e.g. as shown in Fig. 5. Here, the false ceiling 3 is horizontally movable, whereby the pressure difference across the glass plate 7 can be maintained when the mold 6 is transferred from the furnace 1 to the tempering compartment 2. During the transfer phase, the valve 4.3 controls the blow from the duct branch 4.1 up to or at least so close to the effect of tempering blowing that the glass sheet 7 does not have time to deform by bending or hanging downwards. Of course, other arrangements for maintaining the differential pressure effect are also possible during the transfer phase.

In the mold shown in Fig. 4, mechanical benders engaging the edge of the glass sheet 7 are formed by means of articulated levers 9, which turn the edges of the glass sheet downwards even if said pressure difference prevents the edges from bending in a reasonable time and tempering temperature.

In the example of Fig. 7, holes or slots 11 are made in the mold 6, through which air can flow from a higher pressure P2 to a lower pressure Pj. By positioning and shaping the holes or slots 11, this air flow can be controlled so that an enhanced convection effect is achieved at critical bending points.

In the case of Fig. 8, the area of the opening 3.1 and the sealing collar 3.2 is considerably smaller than the area of the ring mold 6, whereby the differential pressure effect can be applied to the center of the glass sheet; while the downwardly bending edge areas are free to bend downwards without being opposed by said differential pressure effect. Thus, even sharp bends can be made to the edge areas of the glass sheet.

The transfer of the glass plate 7 and the mold 6 between the furnace and the tempering compartment can be realized e.g.

Since the furnace parts 1.1. and 1.2 is only needed when the glass sheet begins to bend, the fan 5 does not need to be used at the beginning of the heating cycle if the glass sheet 7 is heated to the final bending temperature only in the bending furnace 1. If instead the glass sheet 7 is heated to or near the bending temperature imported into the bending compartment 1 from the preceding oven compartment, the fan 5 may be running continuously. However, at the end of the bending, especially if the suspended ceiling 3 and the collar 3.2 are relatively tight, the blowing power 5 must be reduced so that the pressure difference between the furnace parts 1.1 and 1.2 does not start to increase when the glass sheet 7 closes the flow path.

The method according to the invention achieves e.g. the following advantages: 1. The glass plate is subjected to mechanical contact only at the edges, so that there are no surface defects of any kind in the central part of the glass, where the surface quality requirements are greatest.

2. The deflection of glass occurs by gravity without any significant contact or force, resulting in elastic deflections and no optical defects in the glass as a result of "discontinuous" bending or depressions caused by contact with the mold surface.

3. The entire glass can be heated to a sufficiently high temperature for tempering, which makes it possible to bend and temper even thin glass.

4. Bending mold technology is cheaper than ceramic molds and 7 86054 easier to implement.

5. Monitoring the temperature and deflection of the glass is easy because the glass is in place. Due to the pressure difference, the effect of gravity is partially eliminated, whereby the bending is also slow and the bending process can be performed calmly without sudden deformations.

6. The heating effect can be applied to critical bending points.

7. Since the method allows bending at high temperatures, the glass sheet can also be formed into difficult bending shapes only by the interaction of the edge mold and the local air jet. Until now, expensive ceramic molds have always been required for difficult bending shapes.

The invention has been described above by means of only some embodiments and it is clear that the details and structural embodiments of the invention may in many ways vary within the scope of the following claims.

Claims (12)

A method of bending a glass sheet comprising the following steps: - a glass sheet (7) is heated in a bending furnace (1) as the softening temperature, - the heated glass sheet (7) is supported on an annular mold (6), - the glass sheet is allowed to bend under the influence of gravity, and - from the oven part (1.1) above the glass plate (7) to be bent, air is circulated to the oven part (1.2) below the glass plate, and in this way a different pressure effect is achieved on opposite sides of the glass dish (7), characterized therein. , with said printing effect, the glass sheet bent to its final shape is supported, which, even at its center region, is heated to a sufficient temperature for curing, which temperature is so high that without said printing effect the center region of the glass sheet would bend and hang too long down. 2. A method according to claim 1, characterized in that at least part of the air circulated below the glass sheet (7) is locally directed towards the lower side of the glass sheet, such that the convection heat effect increases at critical bending points (B). 3. A method according to claim 1 or 2, characterized in that, in order to make the printing effect more effective, an intermediate roof (3) is used in the oven (1), at whose opening (3.1) the ring worm (6) and glass plate (7) are placed. M · · ... 4. A method as claimed in any one of claims 1-3, characterized in that the edge of the glass plate (7) is bent downwards or at a corner, while the center area is raised upright by means of said printing action. 86054 5. A method according to claims 1-4, characterized in that the pressure effects occurring on the opposite sides of the glass sheet are measured and the effect of the air circulation fan (5) is controlled on the basis of said measurement (12). 6. A method according to claims 1-5, characterized in that the bending of the edge of the glass sheet (7) is assisted by tecanical weight means (9). 7. Method according to claim 1 or 3, characterized in that said different printing effect is caused between the opposite surfaces of the glass sheet (7) even during its transfer stage from the oven (1) to the curing section (2). 8. A device for bending a glass plate to which the device belongs: - a bending furnace (1) with heaters for keeping the oven temperature sufficiently high for the bending of the glass plate, and - an annular shape (6) on which the glass plate (7) to be bent is supported in the bending furnace, characterized in that the device also includes: - an intermediate roof (3) which divides the furnace into an upper and a lower compartment (1.1 and 1.2) and which intermediate roof (3) has an opening (3.1) at open center area of the annulus (6): - a pipe or duct system (4) which joins the furnace compartment (1.1) ['· above the intermediate roof (3) with the furnace compartment (1.2) below the intermediate roof, and' a fan system (5) which via said pipe or duct system transmits air from said above-mentioned space (1.1) to the space below (1.2), whereby different compression effect is produced on the opposite sides of the glass sheet (7), which supports the bent glass sheet from below. Device according to claim 8, characterized in! i3 86054, that the edges of the opening (3.1) of the intermediate roof (3) are at least slightly sealed (3.2) against the annular mold (6). Apparatus according to any of claims 8-9, characterized in that the annular mold (6) has shark (11) or or passages which control the air flow from the lower furnace part (1.1) to the upper (1.2). Device according to any of claims 8-10, characterized in that the opening (3.1) of the intermediate roof (3) defines a smaller surface area than the circumference of the annular mold (6), only a part of the lower surface of the glass sheet (7) is subjected to a higher pressure effect (P2) · Device according to claim 8, characterized in that the intermediate roof (3) is movable in a horizontal direction.